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Hi Rafael, Thanks for your quick reply. 1) I already implemented this with dev_pm_ops. I used suspend and resume callbacks whose prototype is like struct dev_pm_ops power_mgmt_ops { .suspend = powermanagement_suspend, .resume = powermanagement_resume } int powermanagement_suspend(device *dev) { } In normal suspend to ram mode it will work. But will it work in case of hibernation also? if yes, since in suspend and resume call backs, only the device structure is provided, so how can then person can identify it is suspend to ram or hibernation? or for hibernation, poweroff and restore function should be implemented which is similar to suspend and resume call backs in case of suspend to ram? Regards Raj > From: rjw@xxxxxxx > To: rajkumar278@xxxxxxxxxxx > Subject: Re: Question about hibernation > Date: Thu, 14 Oct 2010 11:51:05 +0200 > CC: linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx > > On Thursday, October 14, 2010, Raj Kumar wrote: > > > > Hi Rafael, > > > > 1) I have question on system resume that e.g. in device driver let us say for example structure is defined global, > > e.g. > > > > struct dev > > { > > int a; > > > > } dev_t; > > > > > > this structure is global. Now during system suspend, suppose the value of > > > > dev_t.a =2; > > > > So when the resume happens, will the dev_t.a will remain the same i.e. 2? > > Yes, it will. For hibernation, the contents of all memory from before the image > was created is restored during resume. > > > 2) During the system suspend, if the system hibernates, then the message sent from power management core to all drivers is > > PMSG_HIBERNATE and if system suspends to ram, then message sent from power management core to all drivers is PMSG_SUSPEND. > > That was in the old model, which isn't recommended any more. > > Currently, it is recommended that drivers implement callbacks in struct dev_pm_ops, > as described in Documentation/power/devices.txt and Documentation/power/pci.txt. > > Thanks, > Rafael > > > > > From: rjw@xxxxxxx > > > To: rajkumar278@xxxxxxxxxxx > > > Subject: Re: Question about hibernation > > > Date: Fri, 8 Oct 2010 21:31:48 +0200 > > > CC: linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > On Friday, October 08, 2010, you wrote: > > > > > > > > Hi Rafael, > > > > > > Hi, > > > > > > > I am working on device driver whose some part is user space and some part is kernel space. So the user space part > > > > of the driver provides interface to user space applications. > > > > 1) Now, Suppose some user space is application is going on which is accessing the user space driver and user space driver > > > > scheduled some jobs to kernel space, Now suppose system hibernation start, since it freezes all the user space processes > > > > so suppose jobs are not completed yet which are scheduled to kernel space by user space. > > > > > > > > when the kernel space device driver completes the jobs and gives the notification to user space driver, since user space > > > > process is already frozen, so there will be problem if we suspend the driver using suspend and resume. > > > > > > > > right? > > > > > > Yes, there's going to be a problem if the driver is not prepared to handle such situations. > > > > > > Depending of the particular case, one possible approach is to use a PM notifier > > > as described in Documentation/power/notifiers.txt. > > > > > > > 2) The other point I was seeing, when the power management core freezes all the processes before suspending and resuming > > > > devices, it will take some time for freezing and after that if some device driver refuses to suspend, then it will again resume > > > > the whole processes, so latency time be more. right? > > > > > > Yes, it works as described. > > > > > > > 3) Next question is regarding the kernel space threads, when these are frozen during suspend/hibernation? > > > > > > They are frozen immediately after user space has been frozen, but only a > > > handful of kernel threads are frozen. > > > > > > Thanks, > > > Rafael > > > |
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